Many types of lasers use electrodes to convey excitation energy to either gaseous or non-gaseous plasmas. For instance, radio frequency excited gas lasers utilizing electrodes have become a mainstay in a wide variety of industrial, medical, and scientific applications. In particular, molecular gas lasers, such as those based on carbon dioxide gas, use electrodes to excite the gas plasma.
As is typical with gas lasers, gas temperature is a determining factor of equipment size, beam quality, and power levels of operation. For example, the maximum acceptable plasma temperature for a carbon dioxide based laser is approximately 600 Kelvin. Generally, for optimal performance of a laser, certain temperature ranges for operation of laser plasma are preferred. During operation, generation of the laser plasma produces much heat. To maintain optimal temperature ranges for the plasma any excess heat must be extracted from the plasma.
In lasers utilizing electrodes, the plasma generally contacts the surfaces of the electrodes. The electrodes, thus, become a possible candidate for removing heat from the plasma. Some conventional lasers utilize electrode surfaces in contact with the plasma for cooling by actively cooling the electrodes using fluid circulating through the electrodes. Circulating fluid through electrodes, however, complicates assembly and operation, and increases overall laser system package size.
Other conventional lasers have recognized the problems of circulating fluid through electrodes. Unfortunately, with these conventional lasers that do not cool the electrodes with fluid, the electrodes serve a rather limited role in removing heat from the plasmas. Consequently, these conventional lasers have limitations regarding operational power levels or have cooling structures apart from the electrodes. These additional cooling structures also increase laser size and expense, or restrict laser operations. For instance, some conventional lasers actively circulate the plasma gases, which increases laser size and cost. Other conventional lasers use structures that provide surfaces other than those of the electrodes for cooling of the plasmas.
These strictures include bores, rods, or discharge side walls, which complicate laser assembly, increase laser size, and limit laser operation. For instance, discharge sidewalls can restrict expansion of the gas plasma so that standing waves of varying gas density occur in the gas plasma. These standing waves introduce limitations for the operation of the laser such as the frequencies at which the laser can be pulsed.